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Aviation History
1949
1949 - 0340.PDF
-220 FLIGHT FEBRUARY 24TH, 1949 The second S. 11 trainer on a recent flight near the Hague. Fokker S.U Instructor in the Air . . , . friction load on the ailerons is 2 lb, but it probably builds up in the air. la spite of the very large aileron area the effectiveness is not remarkable, although roll performance would be assessed as fairly high for the type of aircraft. Harmonization was quite acceptable. The elevators carry a tab which is at present insufficiently powerful to trim out stick loads and it is understood that this is being remedied. The absence of a rudder trimmer is not important and will only cause a very occasional leg ache, but from the training point of view it might be better to include the trimmer. Maximum speed in level flight at 1,oooft settles at 105 kt indicated, and the nose position appears low like the Prentice, giving a very good view ahead and down. Accurate medium turns call for gentle use of all controls, and there is no feeling of becoming stable in the turn, so here again the Instructor will show up well in its primary role. In steep turns the approaching high-speed stall is indi- cated positively and quite well in advance, and the effect of stalling is always to roll out over the top, not inwards, there to recover at once as stick pressure is released. To aid the pupil various angles of bank are lightly engraved on the windscreen at horizon level. A straight stall occurs at about 50 kt I.A.S. at 3,000ft. Warning is given and, if held, about f of a turn of in- cipient spin occurs before the nose finally drops into a spin proper. With flaps down the stall was similar and occurred perhaps 4 knots slower. Trial of 4 turns of spin (i,opoft lost) in each direction did not bring out any abnprrrial features,; and recovery was rapid and positive. Two spins were suffi- cient foi comfort, following as they did a good Dutch lunch and a spell of aerobatics, otherwise 1 would have tried opposite aileron and more turns. On the prototype it was possible in this way to make the normally steep spin rough and much flatter Recovery was. however, just as positive, though a little slower under these circum-stances. All aerobatic manoeuvres canbe made in the Instructor with two up and at a weight not ex-ceeding 2,395 lb. With three seats occupied, and at anauthorized top weight of 2,560 lb, the aircraft is re-stricted in regard to aerobatics. With the exception of a trueslow roll all normal practices are quite simple. The last 180degrees of the slow roll is hard" to hold because, as is often thecase, rudder tends to run out apart from being rather heavyto use. Other pilots agree with me in this assessment and withthe opinion that on aerobatics the weight of controls becomes rather wearing. The speed recommended is 120 kt at fullthrottle for all except rolls off and flick manoeuvres. These two are made at 130 kt and not more than 70 kt respectively^.About half a dozen approaches and landings of various sorts were tried and I decided that the flaps are insufficiently effec- DATA FOR FOKKER S.I I INSTRUCTOR Lycoming 0-435-A Flat-Six Engine Fixed-pitch Aeromatic v.p. irv wooden airscrew airscrew * *-Weights ' Empty with equipment ... ". 1,730 1b 1,750 IbTwo occupants with parachutes -. ... 400 1b 400 1b ~ Fuel 218 1b 198 1b : Oil •-,,..,- -O-v— '*•> i7lb 27 Ib Gross weight ... ... • .$".."W..; "..,. 2,375 Ib 2,375 1b Wing loading ... . ^ - ... ll.9lb/sqft ll.9lb/sqft Power loading ... \~.7'' -"' ... 12.5 Ib/h.p. 12.5 Ib/h.p.Performance Max speed at S.L,... ... ... ... ... jM4 m.p.h. 134 m.p.h.Cruising speed at S.L . ;.. -jf'' 106 m.p.h. 106 m.p.h. Minimum speed ... 58 m.p.h. 58 m.p.h-Rate of climb at S.L 730ft/min 905ft/min -* Climb to 3,000ft 4.6 min 3.7 min -•" Climb to 6,000ft 10.6 min 8.3 min Climb to 9,000ft 19.1 min 14.5 min Service ceiling 13,100ft 14,500ft Absolute ceiling 15,100ft 16,000ft Take-off run, 5 m.p.h. wind 590ft 4*W)ftLanding run, 5 m.p.h. wind , 490ft 490ft Cruising range ... ... ... 390 miles 350 miles EngineManpower ... 190 h.p. at 2,550 r.p.m. Cruising power ... ... ... ... 110 h.p. at 2,100 r.p.m.Specific fuel consumpt., cruising .... ... ... 0.53 Ib/b.h.j./hr ^ tive and that sideslipping, except in the form of brief swish-tails, does not help. The flaps do produce some air brake effect which checks an otherwise long float period after the round out, and they produce anose-down change of trim. Their area is small, the centrepanel having been removed!r because of the interference itcaused over the tail surfaces, and because the ailerons occupy-ing such a large section of the wing trailing edge. It isthe intention to increase the angular movement at the sametime as the present inconvenient between-seat three-position flap-control lever is modified. Glide approaches at about65 kt give a convenient rate and angle of descent for in-struction, and with full flap the slight increase in steepness en-hances an already good view of the landing path. Rate of Aero-Holland Cessna Bobcats give a background to the S. 11 parked at Ypenburg airfield. B 14
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